Seoul Semiconductor Acriche 120V AC LED

A 120V AC LED may be a good choice where power supply and driver cost and component complexity is an issue.

An LED that runs from 120V AC (o0r 240VAC) is an inciting item in the solid-state low voltage DC universe. No driver, no transformer. Just plug it into the house current and let ‘er rip! Available in 2W 65l (3000K) / 80l (6300K) and 4W 150l (3000K) to 195l (6300K) versions, these devices are fairly powerful and generate good efficacy (between 32 and 40 lumens per watt), not bad, considering there are no other power losses involved from voltage conversion and driver/conditioning. This is roughly the performance of a 50l/w 24VDC CC device operated from a balanced and high efficiency driver/power supply. Not bad.

Color rendering index is 70. At the low end of the good range, and is caused by a weakness in the red end of the spectral distribution. Further, the peak power is virtually right on top of the 575-600 nm of photopic vision. The result is that the 3000K light looks a bit “White” and less “warm” than one might expect.

To put these to the test, I retrofitted a pendant (in my office), which was originally illuminated with 4 – 75 W Halogen lamps (300 watts for the fixture). I used a total of 8 – 4W PCB Mounted Acriche LEDs mounted to 5W radial heat sinks (32 watts). One set of (4) LEDs are aimed up at the ceiling with customized diffuse parabolic reflectors, the other (4) were aimed down into the glass pyramids. Between the two is a metal plate, painted white. The LEDs were then simply wired into the original luminaires wiring, without even taking it down from the ceiling. The original lamps were housed on glass diffusers, within the glass pyramids and topped by sand etched glass plates. All the remains of this are the pyramids, so the retrofit suffers less diffusion loss.

The finished pendant looks the same as it did before the retrofit..

In application, the lumens generated by the 8 LEDs totals 1,200. The original halogen lamps totaled 4,200. However, the amount of light generated in the space, and on the work surface is only diminished by 17%. Considering the pendant was most always dimmed, the amount of actual light being used has not changed.

The end result is a reduction of power use by 88%, with no change in usable light. On top of this, there is no heat, and the whiteness of the light is a welcome change from the dingy beige of the slightly dimmed halogens and all the glass they were forced to push their lumens through. The color is acceptable for general office lighting use, but not warm or good enough for a dining room or color sensitive application.

Now, let’s talk about alternating current and LEDs, and stroboscopic effect (flicker.) The human eye is able to see fluctuation in light emission below a threshold of around 80hz. That puts the 60hz AC sine wave within the range. Since incandescent lamps produce light from heated elements, this is not an issue. The slight cooling of the filament between cycles is small, so light appears to be continuous. LEDs have no such effect. To combat this, AC LED systems use two sets of LEDs, one to either side of the 60hz sine wave (half on and half off at any time). The result is an improved 120hz cycling. For most, this eliminates any visible flicker. As expected, the Acriche uses two reverse parallel strings of LEDs (to create the 120hz AC effect) and by using a lot of them, creates the high voltage drop.

Operation of LEDs on dimmed AC circuits creates conditions that can cause flicker to worsen. Meanswhile, use of an A-B phase connection can be used to eliminate it altogether.

But, does it flicker? No, and yes… At full brightness, when the sine wave is full, the appearance off any flicker is minimal. Using a simple spinning pin wheel test under an incandescent, then a DC LED product, then compared to the AC LED makes the difference readily apparent.

LEDs have a minimum voltage, below which they stop producing light (the Acriche produces just 50% of full light at 85 volts, then drops off rapidly from there.) With each cycle, the voltage drops past this point, causing the LED to shut off for a very small portion of the cycle. As the only source of light in a space, with rapid movement, those sensitive to flicker will likely see this subtle on-off cycling. Those who have not had an issue with flicker of HID, or CFL sources, will not see any more or less with the Acriche. However, when operated on dimmers that chop the sine wave off, the larger gaps in the wave form, coupled with the threshold voltage drop, flicker becomes much more noticeable. This is most visible when something moves quickly in the room, or when the head is turned quickly.

The dimmer effect cannot be readily solved using conventional dimmers. The solution will require more than sine wave chopping, or PWM control. This is an instant where Pulse Amplitude Modulation at a higher frequency would be a significant improvement both dimmed and undimmed. However, this defeats the cost driver behind this LED package.

We encounter a similar issue in sports lighting, where HID flicker is a serious problem in fast moving activities. The use of a 2 or 3 phase lighting system resolves this. If one were to utilize a three phase input (120/208 for example – which has three sine waves 120 degrees apart) to create a 120V x 120V two phase (center neutral) circuit to the luminaire, and connect half the LEDs on the A phase, and the other on the B phase, there would be 6 “ON” events per 60hz “cycle”, or 360 per second, vs. 120, virtually eliminating flicker, even if this were dimmed. Using all three phases would result in 540 on cycles per second, virtually invisible to human vision.

To resolve this in the test installation, the conventional dimmer was replaced with a wire wound 50W, 500K Ohm Rheostat. This simply reduces the voltage to the LEDs without effecting the shape of the sine wave. The result is no increase in flicker when reduced light levels are set. However, the measured loss through this device means that dimming does not reduce energy consumption. At 50% light level, the watts consumed remains roughly the same energy as the full brightness load. Still a significant saving over the halogen lamps.

At full brightness, the LEDs and heat sinks are just warm, measured at just 43 degrees C. Considering these devices are rated to operate at up to 85C (125C tj), it appears these will live a long life in this application.

Recommendation rating = 7 of 10. Very good lumen output, consistency between devices (color and lumens) were good, simplicity of application a real plus. Flicker of 60hz operation problematic for some, aggravated by dimming. This would be an outstanding source for outdoor lighting, and in retrofit accent lighting in spaces with higher ambient light levels, which will mask flicker issues. Would not recommend this to anyone who has serious issues with flicker, such as those who have issues with existing fluorescent or HID sources, or VDT monitors set at under 80hz. I would not recommend using these devices on conventional dimmers.

Actual product performance against manufacturer claims = 9 of 10. Product performs within expectations raised by manufacturer data. Only critical note is that the issue of flicker and dimming issues are not addressed in company literature or specifications. Strongly recommend that the use of A-B phase connection is roadway and outdoor lighting be included in product data, as this resolves flicker issues completely.

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My 10 cents on Acriche.
I have worked on several new architectural fixture lines with the Acriche devices over the part 12 months. I like them lots. Their relatively low Lumens per Watt numbers are offset by their simplicity of use. I have had mutliple Acriches on test in various fixture designs without any significant problems to report to date. It doesn’t work well with phase control dimmers, but there are dedicated line voltage dimming solutions available for it. the standard lens and optic selection is not very wide.
In my opinion the most commonly used part, the 2 Watt – which comes with a standard hex mcpcb footprint – is a retrofit product only, the 2W discrete component being of more use in commercial fixtures and having the benefit of having its power dialed in on the production line via resistors only. One of the problems with taking this type of device to full scale production is that the Vf bin – usually lower in the purchasing priority list – becomes critical as it determines the value of the drive resistor used to set the power of the device. Not all Vf bins are available all the time meaning that the board manufacturer has to vary the drive components on the fly in response to available bins. Not a huge deal, but something that has to be accounted for with a variable purchasing matix.
The biggest benefit is that the Acriche comes UL listed – not recognized – the only discrete LED to have a UL label to the best of my knowledge. I hear it also has an Energy Star approval which automatically puts an Energy Star label on anything it is used in. I am not 100% sure of that second item, I just heard that recently. Energy Star testing is really expensive, so thats a big deal for manufacturers.
For high volume commodity lighting products I have carried out ROI studies and the costs of ownership are slightly higher than the Philips Rebel product. Philips will tell you that the number of electronic connections inside the Acriche package make it more prone to failure with time – a fact that it is hard to argue with.

Seoul have become a very nice LED manufacturer over the last 18 months. I pretty much use Seoul in all my designs these days – I purchase in the US in volume, hold inventory in Asia and farm inventory out to various factories around the world. This is necessary in order to keep inventory of those pesky bins and be consistent across multiple manufacturing locations. Seoul are just a packager – they do not make die. Interestingly, everything I buy from them contains Cree die these days – a big deal in the educated market place right now. I hear rumours from china that the Acriche is going to be discontinued / revised or improved at the end of Q2 this year. I have not heard this from the manufacturer though.
Incidentally, I took delivery of their latest offering two weeks ago – a tiny device which I just measured 103 Lumens per watt from with a minimal heatsink design. Again using Cree die, this makes Seoul the best bang for the buck I have found for certain commercial lighting appications.

Great comments Jon. As a point of reference, my approach is from the perspective of lighting manufacturers who are not going to get into the entire process of building boards up from scratch, and those who will not be using China sourced components. Their is a large market of build-to-order lighting manufacturers in the USA who struggle with the volume processes and complexity of electronics LED integration often represents. The advantage of the mounted LED-on-mcpcb approach is the resisters are already on each of the devices, so nothing more is required. The extra cost is small for small volume product companies (like mine and many many others), compared to the inventory, development, population of boards, and related costs of the more complete product using discrete LEDs. Installation of the MCPCB Acriche is as simple as putting some thermal grease on the back of the board, and screwing it to a proper heat sink – done. This is actually a simpler product than an incandescent or CFL lamp, and for products using diffusers (decorative indoor and outdoor), the need for optics is eliminated.

Their is but one missing component – a plastic mask for the face of the PCB to cover the live components, that could be snapped or glued in place over the board. A little white injection molded plastic part with a smooth cup surrounding the LED would be a nice addition. This will be a difficult part for small manufacturers to create for themselves.

BTW: While I might agree that the number of internal connections is high, creating a greater potential for failure (reflected in the rated life of 35,000 hrs.)… this argument ignores completely the number of connections within every driver/power supply system at the head of a 24VDC product connected to a high voltage system, all prone to damage and failure as well. In fact, of all the LED products I have experienced failures in, the drivers seem to be more of an issue than the LEDs. I rarely come across a failed LED. In fact, I have a drawer full of oddball mcpcb boards with LEDs on them from failed products – rings, linear strips, various grid arrays – all removed from products where the LEDs are fine but the driver and/or integrated power supply failed. I use these with generic drivers to retrofit other fixtures – sort of found object recycling solid-state style!

The Acriche LED in both discrete and in MCPCB configuration are UL listed components, which, as Jon suggests, will significantly improve application simplicity for manufacturers. This would also be an excellent product for custom LED installations.

Leviton has just entered into an agreement to be the sole provider of Molex LED light modules, which use the Acriche LED. They are rumored to be working on a dimmer for the product, per reps at Lightfair, that will be efficient and not impart flicker issues. I have also experimented with using some of the multi-level quiet fan speed controllers, with interesting results. I have had others offer dimmers for these LEDs, but have not had any delivered. A company called Airtech Systems offers a dimmer for the Acriche now: The only issue I have with these dimmers is they consume some power, negating any energy saving from dimmer operation – so the only benefit is light level control. That’s all I have at the moment. I believe there will be several options in the next few months.

Very excited about the future of acriche, but I wish it would hurry up already!! Where’s the 120 lm/w, or even the 80?? Any idea of when that’s headed our way? Anyhow, there’s some additional good news to what was posted above.. the LUXdrive for use with Acriche… http://www.ledsmagazine.com/products/18982

Got this bookmarked, and I’ll be back for updates ;)

Very nice fixture as well! Seems like this LED can be used effectively with a diffuser/shade like your light, which takes off the “edge.”